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Feneyrol, J., Giuliani, G., Ohnenstetter, D., Rondeau, B., Fritsch, E., Fallick, A. E., Ichang'i, D., Omito, E., Rakotondrazafy, M., Ranatsenho, M. & Lallier, F. (2014) New typology and origin of tsavorite based on trace-element chemistry. Eur. J. Mineral. 26 293–308.
Added by: Florent Boucher (2016-04-29 09:26:44) |
| Type de référence: Article DOI: 10.1127/0935-1221/2014/0026-2367 Numéro d'identification (ISBN etc.): 0935-1221 Clé BibTeX: Feneyrol2014 Voir tous les détails bibliographiques  |
Catégories: MIOPS Mots-clés: absorption-spectroscopy, chemical typology, deposits, electron microprobe analysis, garnet, gemmology, gemology, gems, geographic origin, green grossular, kenya, merelani area, mozambique belt, tanzania, tsavorite, UV-Vis-NIR absorption spectra, V/Cr ratio Créateurs: Fallick, Feneyrol, Fritsch, Giuliani, Ichang'i, Lallier, Ohnenstetter, Omito, Rakotondrazafy, Ranatsenho, Rondeau Collection: Eur. J. Mineral. |
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New electron-microprobe analyses of 'tsavorites' from the Neoproterozoic Metamorphic Mozambique Belt deposits allow the characterization of green grossular according to its trace-element chemistry (V, Cr, Mn). Five chemical types are defined: type 1, vanadian grossular with V {>} Cr {>} Mn (in atoms per formula unit); type 2, vanadian grossular with V {>} Mn {>} Cr; type 3, Mn-bearing vanadian grossular with Mn {>} V {>} Cr; type 4, Mn-bearing chromian grossular with Mn {>} Cr {>} V; and type 5, Cr- and Mn-bearing grossular with Cr {>} Mn {>} V. These types are also characterized by different absorption spectra in the ultraviolet-visible-near infrared. Type 1 tsavorite spectra show a total absorption below 430 nm due to the high vanadium contents. Type 2 tsavorite spectra present the classical absorption bands of V. Types 3 and 4 tsavorite spectra display additional shoulders at 407 and 408 nm due to Mn2+, whereas spectra of Cr-bearing types 4 and 5 tsavorite show the two additional bands of Cr3+ at 697 and 701 nm. The different absorption spectra also indicate Fe2+-Ti4+ charge transfer. We measured OH equivalent to 0.08 to 0.38 wt% eq. H2O within the structure. Concentrations of vanadium, chromium and manganese are good chemical "fingerprints" for determining the geographic provenance of economic tsavorite from Kenya, Tanzania and Madagascar.
Added by: Florent Boucher |